Gravity obviously plays a role in human motor control, but it is not easy to isolate. On one hand, the perception and internal representation of gravity in the brain results from a widely distributed sensory process, including the vestibular system, vision, and somatosensory information [1]}. On the other hand, the constant immersive nature of the body in the Earth gravitational field calls for holistic experimental approaches in contrast to focused interventions on isolated body parts. In these settings, participants are exposed to variable gravito-inertial fields generated by human centrifuges or parabolic flights. The rationale behind these experimental approaches rest on Einstein's equivalence principle (see e.g. [2]}, [3]}): Physics in an accelerated spacecraft (1g) is undistinguishable from physics on the ground. It does, however, not mean that the brain does not attempt to identify the possible different sources that give rise to the same consequences. Beyond the brain's role, it is well-known that variable gravity induces various changes in human physiology, typically at the cardiovascular [4]}, neural [5]} and musculoskeletal levels [6]}. In the present work, we do not focus on a particular physiological aspect but rather adopt a global (bio)mechanical point of view. Our main goal is to show that tools derived from mechanics may lead to conserved measurable parameters that the brain can exploit to plan and execute actions instead of relying on an estimate of gravity acquired through a noisy and distributed process.
